Download The Solar System and Beyond

Earth orbits the Sun as the
solar system revolves within
the Milky Way, which is
among billions of galaxies
that make up the universe.
The Solar System
and Beyond
SECTION 1
Earth’s Place in Space
Main Idea Seasons, phases
of the Moon, eclipses,
and tides are caused by
relationships between the
Sun, Earth, and the Moon.
SECTION 2
The Solar System
Main Idea The solar
system is made up of eight
planets and numerous other
objects that orbit the Sun.
SECTION 3
Stars and Galaxies
Main Idea Billions of
galaxies with all their stars
make up the universe.
Why s tudy comets?
Comets, like the one in the photograph, contain ice, rock, and
dust that are as old as the solar system. By studying comets,
scientists learn more about how the solar system formed.
Science Journal
as it orbits the Sun.
438
Aaron Horowitz/CORBIS
Write a short story about what it would be like to ride on a comet
Start-Up Activities
How many stars are in the sky?
On a clear night, the sky is full of sparkling
points of light. With the unaided eye, you can
see hundreds of these sparkles. How many
stars are there?
1. Using white
2.
3.
4.
5.
crayon or chalk
and a ruler,
draw grid lines
on a sheet of
black construction paper,
dividing it into
5-cm squares.
Spill 4 g of rice grains onto the black paper.
Count the number of grains of rice in one
square. Repeat this step with a different
square. Add the number of grains of rice
in the two squares. Divide this number by
two to calculate the average number of
grains of rice in the two squares.
Multiply this number by the number of
squares on the paper to get an estimate of
the number of rice grains on the paper.
Think Critically How could scientists use
a similar method to estimate the number
of stars in the sky?
Planets in the Solar System
Make the following Foldable to
compare and contrast the inner
planets and the outer planets.
STEP 1 Fold one sheet of paper lengthwise.
STEP 2 Fold into thirds.
STEP 3 Unfold and draw overlapping ovals.
Cut the top sheet along the folds.
STEP 4 Label the ovals as shown.
Inner
Planets
Both
Outer
Planets
Construct a Venn Diagram As you read the
chapter, list the characteristics unique to the
inner planets under the left tab. List those
unique to the outer planets under the right tab.
List characteristics that are common to both
inner and outer planets under the middle tab.
Preview this chapter’s content
and activities at
red.msscience.com
439
(c)Morrison Photography, (bkgd)Aaron Horowitz/CORBIS
Learn It!
Knowing how to find answers to questions will
help you on reviews and tests. Some answers can be found in the textbook,
while other answers require you to go beyond the textbook. These answers
might be based on knowledge you already have or things you have
experienced.
Practice It!
Read the excerpt below. Answer the following questions and then discuss them with a partner.
Because summer sunlight strikes at a higher
angle, it is more intense than winter sunlight.
There are also more hours of daylight during
summer than during winter. . . . These two factors
cause summer to be warm. Six months later, when
the part of Earth that you live on is tilted away
from the Sun, you have winter. Autumn and
spring begin when Earth is neither tilted toward
nor away from the Sun.
—from page 441
• What causes seasons such as winter and summer?
• Does winter occur during the same months in both the
northern and southern hemispheres?
• Are winters usually warm and summers usually cold at latitudes
south of the Tropic of Capricorn?
Apply It!
Look at some questions in the Chapter Review. Which questions
can be answered directly from the text?
Which require you to go beyond the text?
440 A
CHAPTER 15 The Solar System and Beyond
Use this to focus on the main ideas as you read the chapter.
Before you read the chapter, respond to the statements
below on your worksheet or on a numbered sheet of paper.
• Write an A if you agree with the statement.
• Write a D if you disagree with the statement.
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After you read the chapter, look back to this page to see if you’ve
changed your mind about any of the statements.
• If any of your answers changed, explain why.
• Change any false statements into true statements.
• Use your revised statements as a study guide.
Before You Read
A or D
Print out a worksheet of
this page at
Statement
1
Earth’s revolution around the Sun causes day
and night to occur.
2
The same side of the Moon always faces Earth.
3
A lunar eclipse occurs when the Moon comes
between Earth and the Sun.
4
As Earth rotates, different places pass through
high and low tide.
5
The orbits of the planets are slightly elliptical.
6
Kilometers are the most useful unit of measure
when discussing objects in our solar system.
7
Mars is the third planet from the Sun and is nicknamed the blue planet.
8
Constellations are groups of stars that form patterns in the sky.
9
The color of a star indicates its temperature.
red.msscience.com
10
After You Read
A or D
Scientists often use astronomical units to measure distances between galaxies.
440 B
Earth’s Place in Space
Earth Moves
■
■
■
Explain Earth’s rotation and
revolution.
Explain why Earth has seasons.
Model the relative positions of
Earth, the Moon, and the Sun
during different lunar phases.
You’ll understand night and day
and the seasons.
Review Vocabulary
axis: the imaginary line around
which a planet or moon rotates
New Vocabulary
•• rotation
•• maria
orbit
eclipse
revolution
•• lunar highlands • tides
Figure 1 The rotation of Earth
around its axis causes night
and day.
You wake up, stretch and yawn, then glance out your window to see the first rays of dawn. By lunchtime, the Sun is high
in the sky. As you sit down to dinner in the evening, the Sun
appears to sink below the horizon. Although it seems like the
Sun moves across the sky, it is Earth that is moving.
Earth’s Rotation Earth spins in space like a twirling figure
skater. Your planet spins around an imaginary line running
through its center called an axis. Figure 1 shows how Earth spins
around its axis.
The spinning of Earth around its axis is called Earth’s
rotation (roh TAY shun). Earth rotates once every 24 h. The Sun
appears each morning due to Earth’s rotation. Throughout the
day, Earth continues to rotate and the Sun appears to move
across the sky. In the evening, the Sun seems to go down because
the place where you are on Earth is rotating away from the Sun.
You can see how this works by standing and facing a lamp.
Pretend you are Earth and the lamp is the Sun. Now, without
pivoting your head, turn around slowly in a counterclockwise
direction. The lamp seems to move across your vision, then disappear. You rotate until you finally see the lamp again. The lamp
didn’t move—you did. When you rotated, you were like Earth
rotating in space, causing different parts of
the planet to face the Sun at different times.
Axis
The rotation of Earth—not movement of the
Sun—causes night and day.
Why does the Sun appear
to move across the sky?
Because the Sun only appears to move
across the sky, this movement is called
apparent motion. Stars, planets, and the
Moon also appear to move across the sky.
You might have observed the Moon rise and
set, just like the Sun. How can you recognize
apparent motion that results from Earth’s
rotation?
Earth´s
rotation
440
CHAPTER 15 The Solar System and Beyond
September
23.5
June
December
Figure 2 Earth takes one year to
March
revolve around the Sun.
Infer why Earth’s seasons occur in a
pattern.
Earth’s Revolution Earth rotates in space, but it also moves
in other ways. Like an athlete running around a track, Earth
moves around the Sun in a regular, curved path called an orbit.
The movement of Earth around the Sun is known as Earth’s
revolution (reh vuh LEW shun). A year on Earth is the time it
takes for Earth to complete one revolution, as seen in Figure 2.
Seasons Who doesn’t love summer? The long, warm days are
great for swimming, biking, and relaxing. Why can’t summer
last all year? Blame it on Earth’s axis and revolution around the
Sun. The axis is not straight up and down like a skyscraper—it
is slightly tilted. It’s because of this tilt and Earth’s revolution
that you experience seasons.
Look at Figure 2. Summer occurs when your part of Earth is
tilted toward the Sun. During summer, sunlight strikes at a
higher angle than it does during winter. You might have noticed
that when you go outside at noon, your shadow is shorter during summer than during winter. Because summer sunlight
strikes at a higher angle, it is more intense than winter sunlight.
There also are more hours of daylight during summer than during winter. These two factors cause summer to be warm. Six
months later, when the part of Earth that you live on is tilted
away from the Sun, you have winter. During winter, sunlight
strikes at a lower angle than during summer. The days are short,
and the nights are long. Autumn and spring begin when Earth is
neither tilted toward nor away from the Sun.
Modeling Earth’s
Seasons
Procedure
1. Place a shaded lamp on a
table in your classroom.
The lamp represents the
Sun. Turn on the lamp, and
turn off the overhead lights.
2. Using a globe, model
Earth’s position during
each of the four northern
hemisphere seasons.
Remember to tilt the globe
so that its axis makes an
angle of about 23.5° from
straight up.
Analysis
During which season did the
light shine most intensely
on the northern hemisphere
of the globe? During which
season did it shine least
intensely?
SECTION 1 Earth’s Place in Space
441
Earth’s Moon
Astronaunt Dr. Mae
Jemison was a Science
Mission Specialist on the
space shuttle Endeavor.
While in space, she studied
bone cells and biofeedback.
On Earth, she directs the
Jemison Institute, which
brings new technologies to
developing countries. If you
want to be an astronaunt,
like Dr. Jemison, you’ll need
to exercise your mind and
your body.
Does the Moon look perfect to you? Many ancient people
thought that the Moon’s surface was perfectly smooth. This
belief was common until about 400 years ago when a scientist
named Galileo looked at the Moon through his telescope.
Galileo saw large, mountainous regions with many craters. He
also saw smooth, dark regions. The mountainous areas of the
Moon are called lunar highlands. The lunar highlands are
about 4.5 billion years old. The many craters on the lunar highlands formed when meteorites hit the Moon just after it
formed. The smooth, dark regions of the Moon are called
maria, which is the Latin word for sea. The maria formed when
lava erupted from the Moon’s interior and cooled in low areas
on its surface.
Orbiting Earth While Earth revolves around the Sun, the
Figure 3 When you ride on a
merry-go-round, it takes the same
amount of time for you to rotate as
it does for you to revolve around
the center.
Explain how this is similar to the
way the Moon rotates and revolves.
Moon and a variety of human-made objects orbit Earth. The
Moon revolves around Earth once every 27.3 days. It has an
average distance from Earth of 384,400 km. This is like traveling
from Los Angeles to New York and back again 49 times. Other
objects orbit much closer to Earth than the Moon does. These
objects include the International Space Station, a wide variety of
satellites, and much debris. The debris, often called space junk,
consists of parts from old rockets and a variety of discarded
tools and equipment.
Rotation and Revolution How long
does it take for the Moon to rotate one time?
The answer is 27.3 days—exactly the same
amount of time that it takes for the Moon to
revolve around Earth one time. Because the
Moon rotates and revolves at the same rate,
the same side of the Moon always faces Earth.
The side of the Moon that faces Earth is
called the near side. The opposite side of the
Moon is called the far side. If you’ve ever ridden on a playground merry-go-round, you
rotated and revolved somewhat like the
Moon. Look at Figure 3. When you ride on a
merry-go-round, your body rotates at exactly
the same rate as it revolves. You always face
the center of the merry-go-round, just like
the Moon always keeps the same face toward
Earth.
442
CHAPTER 15 The Solar System and Beyond
Moon Phases How many different moon shapes have you
seen? Have you seen the Moon look round or maybe like a half
circle? Although the Moon looks different at different times of
the month, it doesn’t change. What does change is the way the
Moon appears from Earth. These changes are called phases of
the Moon. Figure 4 shows the various phases of the Moon.
Figure 4 When the moon
phases get larger, they are said to
be waxing. When the moon phases
get smaller, they are waning.
Explain the difference between
a waxing crescent and a waning
crescent.
Light from the Sun The Moon does not produce its own light.
The light that comes to Earth from the Moon is reflected sunlight.
Also, just as half of Earth experiences day while the
other half experiences night, one half of the Moon
is lit by the Sun while the other half is dark.
The Lunar Cycle The phase of the Moon that
you see on any given night depends on the relative positions of the Moon, the Sun, and Earth in
space. These positions change because the Moon
is continually revolving around Earth as Earth
revolves around the Sun. It takes the Moon about
one month to go through its phases. During that
time, called a lunar cycle, you see different portions of the daylight side of the Moon.
The lunar cycle begins with new moon. During
new moon, the Moon is between Earth and the
Sun. Half of the Moon is lit by the Sun, but this half
can’t be seen from Earth. For about two weeks after
new moon, the portion of the lit side of the Moon
that can be seen from Earth increases. At first, only
a small crescent is visible. Then, you see the first
quarter moon followed by the gibbous moon.
Finally, the Moon is full. At full moon, Earth is
between the Moon and the Sun, and the entire near
side of the Moon is visible from Earth. For about
two weeks after full moon, the moon phase appears
to get smaller. The phase gradually changes from a
gibbous moon, to a third quarter moon, crescent
moon, and finally new moon again.
New moon
Waxing crescent
Waning crescent
First quarter
Third quarter
Waxing gibbous
Waning gibbous
Full moon
What is the lunar cycle?
Recall that the near side of the Moon always
faces Earth. This means that during the new moon
phase, the far side of the Moon is lighted by the
Sun. The far side of the Moon is lighted just as
much as the near side is. The far side can’t be seen
from Earth because it is always facing away from it.
SECTION 1 Earth’s Place in Space
443
Lick Observatory
Figure 5 During a solar eclipse, the Moon
moves directly between the Sun and Earth. The
Sun’s corona is visible during a total solar eclipse.
Identify the phase that the Moon must be in for a
solar eclipse to occur.
Sun’s corona
Area of partial
eclipse
Sun
Moon
Area of total
eclipse
Fra
nco
is G
ohie
r/Ph
oto
Res
ear
che
rs
Topic: Eclipse Data
Visit red.msscience.com for Web
links to information about future
solar and lunar eclipses.
Activity Find out when you will
next be able to observe an eclipse
in your region.
Earth
Solar Eclipse Have you ever tried to watch TV with someone
standing between you and the screen? You can’t see a thing. The
picture from the screen can’t reach your eyes because someone is
blocking it. Sometimes the Moon is like that person standing in
front of the TV. It moves directly between the Sun and Earth and
blocks sunlight from reaching Earth. The Moon’s shadow travels
across parts of Earth. This event, shown in Figure 5, is an example
of an eclipse (ih KLIHPS). Because it is an eclipse of the Sun, it is
known as a solar eclipse. The Moon is much smaller than the Sun,
so it casts a small shadow on Earth. Sunlight is blocked completely
only on the small area of Earth where the Moon’s darker shadow
falls. In that area, the eclipse is said to be a total solar eclipse.
What causes solar eclipses?
Due to the small size of the shadow—about 269 km wide—
only a lucky few get to experience each solar eclipse. For the few
minutes the total eclipse lasts, the sky darkens, flowers close, and
some planets and brighter stars become visible. The Sun’s spectacular corona, its pearly white, outermost layer, can be
observed. Far more people will be in the lighter part of the
Moon’s shadow and will experience a partial solar eclipse.
WARNING: Never look at the Sun during an eclipse. You might
damage your eyes.
444
CHAPTER 15 The Solar System and Beyond
Figure 6 During a lunar
eclipse, Earth is between the
Sun and the Moon. The Moon
often appears red during a
lunar eclipse.
Infer why lunar eclipses are
observed more frequently than
solar eclipses.
Sun
Moon
Earth
Lunar Eclipse Sometimes Earth is directly between the Sun
and the Moon. When Earth’s shadow falls on the Moon, an
eclipse of the Moon occurs. This is called a lunar eclipse.
Everyone on the nighttime side of Earth, weather permitting,
can see a lunar eclipse. When eclipsed, the full moon becomes
dim and sometimes turns deep red, as shown in Figure 6.
Lunar eclipse
Tides The Moon’s gravity pulls on Earth. One effect of the Moon’s
gravity is tides. Tides are an alternate rise and fall in sea level. They
are most noticeable along a beach. At high tide, water moves farther
onto the beach. At low tide, water moves off the beach.
Tides occur because the Moon’s gravity decreases with distance
from the Moon. Places on Earth closer to the Moon are pulled
harder than places that are farther from the Moon. The Moon’s
gravity holds Earth in its path around the center of mass of the
Earth-Moon system. At places on Earth that are closer to the Moon,
the Moon’s gravity is a bit stronger than it needs to be to hold Earth.
At places on Earth that are farther from the Moon, the Moon’s
gravity is a bit weaker than it needs to be.
The small differences in the Moon’s gravity cause the water in Earth’s oceans to form
two bulges, shown in Figure 7. One bulge is
High tide
on the side of Earth toward the Moon, and
one is on the opposite side. These bulges of
water are the high tides. The areas of Earth
that are neither toward nor away from the
Moon are the low tides. As Earth rotates, different places pass through high and low tide.
Figure 7 Tides form because
the Moon’s gravity pulls harder on
parts of Earth that are closer to it.
Two tidal bulges occur—one on
the side of Earth closest to the
Moon, and one on the opposite
side of Earth.
Center of mass
High tide
Moon
Path of the Moon
Jerry Lodriguss/Photo Researchers
and
Spring tides occur
when the Sun,
Moon, and Earth
are aligned.
and
Neap tides occur
when the Sun,
Moon, and
Earth form a
right angle.
Figure 8 Because the Moon
revolves around Earth, spring tides
and neap tides each occur about
twice each month.
The Sun’s Effect on Tides The Sun also affects tides on
Earth. Because the Sun is much farther from Earth, it has about
half as much tide-generating force as the Moon. When the Sun,
Earth, and the Moon are lined up, high tides are higher and low
tides are lower. This is called spring tide, as shown in Figure 8.
Spring tides occur because the Moon’s gravity and the Sun’s
gravity combine to produce a greater effect. When the Sun,
Earth, and the Moon form a 90° angle, high tides are lower and
low tides are higher. This condition, also shown in Figure 8, is
called neap tide. During neap tide, the Sun’s gravity reduces the
tide-generating effect of the Moon’s gravity.
Summary
Earth Moves
Seasons occur because of Earth’s tilted axis
and Earth’s revolution around the Sun.
•
Earth’s Moon
The Moon has many surface features including craters, maria, and lunar highlands.
Different moon phases occur depending on
the positions of the Sun, Earth, and the Moon.
•
•
Tides
The Moon has the greatest effect on Earth’s
tides. The Sun has a lesser effect.
•
446
CHAPTER 15 The Solar System and Beyond
Self Check
1.
2.
3.
4.
Define Earth’s revolution and rotation.
Explain why lunar eclipses occur during a full moon.
Compare and contrast spring tides and neap tides.
Think Critically What would seasons be like if Earth’s
axis were tilted at a higher angle (more than 23.5°)?
5. Research Information Some scientific knowledge is
very old, yet it still is correct today. Do research to
learn how much the ancient Mayan civilization knew
about the length of a year.
red.msscience.com/self_check_quiz
Mhh n Phases
The Moon is Earth’s nearest neighbor in
space. The Sun, which is much farther away,
is the source of light that reflects off of the
moon. In this lab, you’ll observe how the
positions of the Sun, the Moon, and Earth
cause the different phases of the Moon.
Real-World Question
How do the positions of the Sun, the Moon,
and Earth affect the phases of the Moon?
Goals
■ Model and observe moon phases.
■ Record and label phases of the Moon.
■ Infer how the positions of the Sun, the
Moon, and Earth affect phases of the Moon.
Materials
drawing paper (several sheets)
softball
flashlight
Safety Precautions
Procedure
1. Turn on the flashlight and darken other
lights in the room. Select a member of your
group to hold the flashlight. This person will
be the Sun. Select another member of your
group to hold up the softball so that the
light shines directly on the ball. The softball
will be the Moon in your experiment.
2. Everyone else represents Earth and should
sit between the Sun and the Moon.
3. Observe how light shines on the Moon.
Draw the Moon, being careful to add shading to represent its dark portion.
4. The student who is holding the Moon should
begin to walk in a slow circle around the
group, stopping at least seven times at
different spots. Each time the Moon stops,
observe it, draw it, and shade in its dark
portion.
Conclude and Apply
1. Compare and contrast your drawings
with those of other students. Discuss similarities and differences in the drawings.
2. In your own words, explain how the
positions of the Sun, the Moon, and Earth
affect the phase of the Moon that is visible
from Earth.
3. Compare your drawings with Figure 4.
Which phase is the Moon in for each drawing? Label each drawing with the correct
moon phase.
Use your drawings to make a poster
explaining phases of the Moon. For more
help, refer to the Science Skill Handbook.
LAB
447
Doug Martin
The Solar System
Distances in Space
■
■
Compare and contrast the planets and moons in the solar system.
Explain that Earth is the only
planet known to support life.
Much can be learned about Earth by
studying the solar system.
Review Vocabulary
system: a portion of the universe
and all of its components,
processes, and interactions
New Vocabulary
system
•• solar
•• comet
astronomical unit
meteorite
Imagine that you are an astronaut living in the future, doing
research on a space station in orbit around Earth. You’ve been
working hard for a long time and need a vacation. Where will
you go? How about a tour of the solar system? The solar system,
shown in Figure 9, is made up of eight planets and numerous
other objects that orbit the Sun, all held in place by the Sun’s
immense gravity.
What holds the solar system together?
The planets in the solar system revolve around the Sun in
elliptical orbits. The orbits of most of the planets are only
slightly elliptical. They are almost circular. Mercury’s orbit is
more elliptical. Its orbit is similar to an oval or a slightly flattened circle.
Figure 9 The Sun is the center of the solar system, which is made
up of eight planets and other objects that orbit the Sun.
Compare and contrast the sizes of the different planets.
Uranus
Neptune
Saturn
448
CHAPTER 15
Jupiter
Measuring Space Distances in space are hard to imagine
because space is so vast. Suppose you had to measure your pencil, the hallway outside your classroom, and the distance from
your home to school. Would you use the same unit for each
measurement? No. You probably would measure your pencil in
centimeters. You would use something bigger to measure the
length of the hallway, such as meters. You might measure the
trip from your home to school in kilometers. Larger units are
used to measure longer distances. Imagine trying to measure the
trip from your home to school in centimeters. If you didn’t lose
count, you’d end up with a huge number.
Topic: Space Technology
Visit red.msscience.com for Web
links about technology that is used
to explore space.
Activity Create a concept map
that explains why technology is
essential to science.
Astronomical Unit Kilometers are fine for measuring long
distances on Earth, such as the distance from New York to
Chicago (about 1,200 km). Even bigger units are needed to
measure vast distances in space. One such measure is the
astronomical (as truh NAH mih kul) unit. An astronomical
unit equals 150 million km, which is the average distance from
Earth to the Sun. Astronomical unit is abbreviated AU. If something is 3 AU away from the Sun, then the object is three times
farther from the Sun than Earth is. The AU is a convenient unit
for measuring distances in the solar system.
Why is the astronomical unit useful for
measuring distances in the solar system?
Mercury
Venus
Earth
Mars
Sun
SECTION 2 The Solar System
449
Touring the Solar System
Observing Planets
Procedure
1. Research which planets
currently are visible in the
night sky.
2. Select a planet to watch for
three to four weeks. You
might choose Jupiter,
Saturn, Mars, or Venus.
3. Observe the planet at the
same time each clear
night. Note the planet’s
position compared to background stars.
4. You might want to use
a camera to photograph
the planet and background
stars each night.
Analysis
1. Did the planet move
against the background
stars? If so, did it move
from west to east or from
east to west?
2. How can you explain the
planet’s
movement?
Now you know a little more about how to measure distances
in the solar system. Next, you can travel outward from the Sun
and take a look at the objects in the solar system. Maybe you can
find a nice destination for your next vacation. Strap yourself
into your spacecraft and get ready to travel. It’s time to begin
your journey. What will you see first?
Inner Planets
The first group of planets you pass is the inner planets.
These planets are mostly solid, with minerals similar to those
on Earth. As with all the planets, much of what is known
comes from spacecraft that send data back to Earth. Various
spacecraft took the photographs shown in Figure 10 and the
rest of this section. Some were taken while in space and others
upon landing.
Mercury The first planet that you will visit is the one that is
closest to the Sun. Mercury, shown in Figure 10, is the smallest
planet. Its surface has many craters. Craters form when meteorites, which are chunks of rock or metal that fall from the sky,
strike a planet’s surface. You will read about meteorites later in
this section. Because of Mercury’s small size and low gravity,
gases that could form an atmosphere escape into space. The lack
of an atmosphere and the closeness of this planet to the Sun
cause great extremes in temperature. Mercury’s surface temperature can reach 425°C during the day and drop to 170°C at
night, making the planet unfit for life.
Why do surface temperatures on Mercury vary
so much?
Figure 10 Mercury and Venus
Venus You won’t be able to
are closer to the Sun than Earth is.
Like the Moon, Mercury’s surface
is scarred by craters.
450
Earth’s closest neighbor,
Venus, is covered in clouds.
CHAPTER 15 The Solar System and Beyond
(l)USGS/Science Photo Library/Photo Researchers, (r)NASA/Science Source/Photo Researchers
see much at your next stop,
also shown in Figure 10.
Venus, the second-closest
planet to the Sun, is hard
to see because its surface
is surrounded by thick
clouds. These clouds trap
the solar energy that reaches
the surface of Venus. That
energy causes surface temperatures to hover around
472°C—hot enough to bake
a clay pot.
Earth Home sweet home. You’ve reached Earth, the third
planet from the Sun. You didn’t realize how unusual your home
planet was until you saw other planets. Earth’s surface temperatures allow water to exist as a solid, a liquid, and a gas. Also,
ozone in Earth’s atmosphere works like a screen to limit the
number of ultraviolet (ul truh VI uh lut) rays that reach the
planet’s surface. Ultraviolet rays are harmful rays from the Sun.
Because of Earth’s atmosphere, life can thrive on the planet. You
would like to linger on Earth, shown in Figure 11, but you have
six more planets to explore.
Mars Has someone else been here? You see signs of earlier visits to Mars, the fourth of the inner planets. Tiny robotic explorers have been left behind. However, it wasn’t a person who left
them here. Spacecraft that were sent from Earth to explore Mars’s
surface left the robots. If you stay long enough and look around,
you might notice that Mars, shown in Figure 12, has seasons and
polar ice caps. Signs indicate that the planet once had abundant
liquid water. Water might even be shaping the surface of Mars
today. You’ll also notice that the planet looks red. That’s because
the sediment on its surface contains iron oxide, which is rust.
Two small moons, Phobos and Deimos, orbit Mars.
Figure 11 As far as scientists
know, Earth is the only planet that
supports life.
Figure 12 Mars often is called
the Red Planet.
Explain what causes Mars’s
surface to appear red.
SECTION 2 The Solar System
451
(tr)CORBIS, (bl)NASA, (br)USGS/TSADO/Tom Stack & Assoc.
Asteroid Belt Look out for asteroids. On the next
part of your trip, you must make your way through
the asteroid belt that lies between Mars and the next
planet, Jupiter. As you can see in Figure 13, asteroids
are pieces of rock made of minerals similar to those
that formed the rocky planets and moons. In fact,
these asteroids might have become a planet if it
weren’t for the giant planet, Jupiter. Jupiter’s huge
gravitational force might have prevented a small
planet from forming in the area of the asteroid belt.
The asteroids also might be the remains of larger
bodies that broke up in collisions. The asteroid belt
separates the solar system’s planets into two
groups—the inner planets, which you’ve already visited, and the outer planets, which are coming next.
What are asteroids?
Figure 13 This close-up of the
asteroid Gaspra was taken by the
Galileo spacecraft in 1991.
Describe Gaspra’s surface features.
Figure 14 Jupiter is the largest
Outer Planets
Moving past the asteroids, you come to the outer planets.
The outer planets are Jupiter, Saturn, Uranus, and Neptune. Let’s
hope you aren’t looking for places to stop and rest. Trying to
stand on most of these planets would be like trying to stand on
a cloud. That’s because all of the outer planets are huge balls of
gas called gas giants. Each might have a solid core, but none of
them has a solid surface. They have rings surrounding them that
are made of dust and ice.
The gas giants have many moons that orbit the planets just
like Earth’s Moon orbits Earth. Three of Jupiter’s moons
(Ganymede, Callisto, and Io) are larger than Earth’s Moon. Also,
Saturn’s largest moon, Titan, is larger than Earth’s Moon.
planet in the solar system.
Jupiter If you’re looking for excitement, you’ll find it on
Jupiter, which is the largest planet in the solar system and
the fifth from the Sun. It also has the shortest day—less
than 10 h long—which means this giant planet is spinning
faster than any other planet. Watch out for a huge, red
whirlpool near the middle of the planet! That’s the Great
Red Spot, a giant storm on Jupiter’s surface. Jupiter, shown
in Figure 14, looks like a miniature solar system. It has 63
moons. One called Ganymede (GA nih meed) is larger
than the planet Mercury. Ganymede, along with two other
moons, Europa and Callisto, might have liquid water under
their icy crust. Another of Jupiter’s moons, Io, has more
active volcanoes than any other object in the solar system.
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CHAPTER 15 The Solar System and Beyond
(t)JPL/TSADO/Tom Stack & Assoc., (b)CORBIS
Saturn You might have thought that Jupiter was
unusual. Wait until you see Saturn, the sixth planet
from the Sun. You’ll be dazzled by its rings, shown in
Figure 15. Saturn’s several broad rings are made up of
hundreds of smaller rings, which are made up of
pieces of ice and rock. Some of these pieces are like
specks of dust. Others are many meters across. Saturn
is orbited by at least 47 moons, the largest of which is
Titan. Titan has an atmosphere that resembles the
atmosphere on Earth during primitive times. Some
scientists hypothesize that Titan’s atmosphere might
provide clues about how life formed on Earth.
Uranus After Saturn, you come to Uranus, the seventh planet
from the Sun. Uranus warrants a careful look because of the
interesting way it spins around its axis. The axis of most planets
is tilted just a little, somewhat like the handle of a broom that is
leaning against a wall. Uranus, also shown in Figure 15, is nearly
lying on its side. Its axis is tilted almost even with the plane of its
orbit like a broomstick lying on the floor. Uranus’s atmosphere is
made mostly of hydrogen with smaller amounts of helium and
methane. The methane gives Uranus its distinctive bluish-green
color. Uranus has rings and is thought to have at least 27 moons.
Figure 15 Saturn and Uranus
are two of the four gas giant
planets.
How can you model distances in the solar system?
T
he distances between the planets
and the Sun are unimaginably large
but definitely measurable. Astronomers
have developed a system of measurement to describe these distances in
space. Could you represent these vast
distances in a simple classroom model?
Use your knowledge of SI and your
ability to read a data table to find out.
Identifying the Problem
The table shows the distances of the
planets and asteroid belt from the Sun.
Notice that the inner planets are fairly
close together, and the outer planets are
far apart. Study the distances carefully,
then answer the questions.
Solving the Problem
1. How can you make
a scale model of
the solar system
that will fit in your
classroom? What
unit will you use
to show the
distances?
2. Show the conversion between
astronomical
units and the unit
you use for your
model.
Solar System Data
Planet
Distance from
the Sun (AU)
Mercury
0.39
Venus
0.72
Earth
1.00
Mars
1.52
Asteroid belt
2–4
Jupiter
5.20
Saturn
9.54
Uranus
19.19
Neptune
30.07
SECTION 2 The Solar System
453
(t)ASP/Science Source/Photo Researchers, (b)NASA/JPL/Tom Stack and Assoc.
from the Sun. Neptune’s atmosphere is composed of hydrogen,
helium, and methane. The methane gives the planet a blue color.
In 1989, Voyager 2 sent pictures of Neptune showing a Great
Dark Spot in its atmosphere. The spot was gone when observations were made using the Hubble Space Telescope in 1994.
Neptune is the last of the big, gas planets with rings around it. It
has 13 moons. Triton, the largest of these, has geysers that shoot
gaseous nitrogen into space. The low number of craters on
Triton indicates that lava still flows onto its surface.
Neptune
Figure 16 Neptune, the
outermost planet, appears blue
because of methane gas in its
atmosphere.
Dwarf Planets Pluto was known as the ninth planet from
the Sun for 76 years, from its discovery in 1930 until August
2006. In 2006, the International Astronomical Union created a
new category called dwarf planets. Pluto was placed in this new
category along with two other objects named Ceres and Eris.
Many scientists believe that Pluto has a small, rocky core with a
frozen crust. Ceres is the smallest dwarf planet and is located
in the asteroid belt. Eris is an icy object that reaches twice as
far from the Sun as Pluto when it’s in the most distant part of
its orbit. Its orbit is so elliptical that it is similar to the orbits
of comets.
Comets
A comet is a large body of ice and rock that travels around
the Sun in an elliptical orbit. Comets might originate from a
cloud of objects far beyond the orbit of Pluto known as the Oort
Cloud. This belt is 50,000–100,000 AU from the Sun. Some
comets return to the Kuiper belt, just beyond the orbit of
Neptune. As a comet approaches the Sun, solar radiation
changes some of the ice into gas. Solar winds blow gas and dust
away from the comet, forming a bright tail, shown in Figure 17.
Why do comets have tails?
Figure 17 Solar wind is a
stream of charged particles moving
away from the Sun. Comet tails
point away from the Sun because
they are pushed by solar wind.
454
(t)NASA/JPL, (b)Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility/NASA
Neptune Neptune, shown in Figure 16, is the eighth planet
Meteorites Occasionally, chunks of
extraterrestrial rock and metal fall to
Earth. Meteorites are any fragments
from space that survive their plunge
through the atmosphere and land on
Earth’s surface. Small ones are no bigger than pebbles. The one in Figure 18
has a mass of 14.5 metric tons.
Hundreds of meteorites fall to Earth
each year. Luckily, strikes on buildings
or other human-made objects are rare.
In fact, only a tiny fraction of the meteorites that fall are ever found. Scientists
are extremely interested in those that
are, because they yield important clues from space. For example,
many seem to be about 4.5 billion years old, which provides a
rough estimate of the age of the solar system. Several thousand
meteorites have been collected in Antarctica, where moving ice
sheets concentrate them in certain areas. Any rock seen on an ice
sheet in Antarctica is probably a meteorite, because few other
rocks are exposed. Meteorites can be one of three types—irons,
stones, and stoney-irons. Irons are almost all iron, with some
nickel mixed in. Stones are rocky. The rarest, stoney-irons, are a
mixture of metal and rock.
Summary
Distances in Space
The planets in the solar system orbit around
the Sun.
Distances in the solar system are vast.
Scientists measure these distances using the
astronomical unit (AU).
•
•
Inner Planets
The inner planets are solid, rocky planets.
Earth is the only planet known to support life.
•
•
•
•
•
Outer Planets
Jupiter, Saturn, Uranus, and Neptune are gas
giants that have ring systems.
Dwarf planets include Ceres, Pluto, and Eris.
Comets
Comets are bodies of ice and rock that orbit
the Sun.
Figure 18 This meteorite on
display at the American Museum of
Natural History in New York has a
mass of 14.5 metric tons.
Explain why meteorites are rare.
Self Check
1. Explain why the planets and other objects in the solar
system orbit around the Sun.
2. List the planets in the solar system in order starting
with the planet that is closest to the Sun.
3. Compare and contrast the moons that were discussed
in this chapter.
4. Infer why carbon dioxide ice exists on Mars but not Earth.
5. Think Critically Earth has abundant life. Do you think
that other planets or moons might support life? If so,
which ones? Which characteristics of the planets or
moons might be conducive to life?
6. Compare and contrast Earth to other planets in terms
of size, composition, distance from the Sun, and surface features. You might want to make a table to
record your data.
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455
AP/Wide World Photos
Stars and Galaxies
Stars
■
■
■
Explain why stars appear to
move across the sky.
Describe some constellations.
Explain the life cycle of stars.
Understanding the vastness of the
universe will help you to appreciate
Earth’s place in space.
Review Vocabulary
star: a large, spherical mass of
gas that gives off light and other
types of radiation; the Sun is a
typical star
New Vocabulary
•• constellation
•• galaxy
supernova
light-year
Every night, a new world opens to you as the stars come out.
Stars are always in the sky. You can’t see them during the day
because the Sun’s light makes Earth’s atmosphere so bright that
it hides them. The Sun is a star, too. It is the closest star to Earth.
Each night the stars appear to move across the sky. This happens
because Earth is rotating around its axis. The stars that can be
seen in the sky also change with the season as Earth revolves
around the Sun.
Constellations Ursa Major, Ursa Minor, Orion, Taurus—do
these names sound familiar? They are constellations (kahn stuh
LAY shunz), or groups of stars that form patterns in the sky.
Figure 19 shows some constellations.
Constellations are named after animals, objects, and
people—real or imaginary. Many of the names that early Greek
astronomers gave to the constellations are still in use. However,
throughout history, different groups of people have seen different things in the constellations. In early England, people
thought the Big Dipper and the constellation Ursa Major looked
like a plow. Native Americans saw a horse and rider. To the
Chinese, it looked like a governmental official and his helpers
moving on a cloud. What image does the Big Dipper bring to
your mind?
Figure 19 Find the Big
Dipper in the constellation
Ursa Major.
Explain why people call it
the Big Dipper.
Ursa
Minor
Ursa
Major
Cepheus
Polaris
Cassiopeia
456
CHAPTER 15 The Solar System and Beyond
Starry Colors Although they look similar from Earth, stars
are different colors. The color of a star is a clue about its temperature. Just as the red flames in a campfire are cooler, red stars are
the coolest visible stars. Yellow stars have medium temperature.
Bluish-white stars, like the blue flames on a gas stove, are the
hottest.
How is a star’s color related to its temperature?
Stars also vary in size. Most of the stars in the universe are small.
The Sun is a yellow, medium-sized star. Betelgeuse (BEE tul joos)
is much bigger than the Sun. If this huge star were in the
same place as the Sun, it would swallow Mercury, Venus, Earth,
and Mars.
Apparent Magnitude Look at the sky on a clear night and
you can easily notice that some stars are brighter than others. A
system called apparent magnitude is used for classifying how
bright a star appears from Earth. The dimmest stars that are visible to the unaided eye measure 6 on the apparent magnitude
scale. A star with an apparent magnitude of 5 is 2.5 times
brighter. The smaller the number is, the brighter the star is. The
brightest star in the sky, Sirius, has an apparent magnitude of
1.5, and the Sun’s apparent magnitude is 26.7.
Compared to other stars, the Sun is medium in size and temperature. It looks so bright because it is so close to Earth.
Apparent magnitude is a measure of how bright a star looks
from Earth but not a measure of its actual brightness, known as
absolute magnitude. As Figure 20 shows, a small, close star
might look brighter than a giant star that is far away.
Modeling
Constellations
Procedure
1. Draw a dot pattern of a constellation on a piece of black
construction paper.
Choose a known constellation or make up your own.
2. With an adult’s help, cut off
the end of a cardboard
cylinder such as an oatmeal
box. You now have a cylinder with both ends open.
3. Place the cylinder over the
constellation. Trace around
the rim. Cut the paper along
the traced line.
4. Tape the paper to the end
of the cylinder. Using a pencil, carefully poke holes
through the dots on the
paper.
5. Place a flashlight inside the
open end of the cylinder.
Darken the room and
observe your constellation
on the ceiling.
Analysis
1. Turn on the overhead light
and view your constellation
again. Can you still see it?
Why or why not?
2. The stars are always in the
sky, even during the day.
How is the overhead light
similar to the
Sun? Explain.
Figure 20 This flashlight looks
brighter than the car headlights
because it is closer. In a similar
way, a small but close star can
appear brighter than a more
distant, giant star.
SECTION 3 Stars and Galaxies
457
Dominic Oldershaw
White dwarf
Main sequence
star
s stars
ll mas
a
m
S
Black dwarf
Giant
or
Supergiant
Neutron star
La
Protostar
r
ge
ma
ss s
ta rs
ss
L arg e m a
Supernova
Nebula
st a r
s
Ver
y la
rge
ma
ss
sta
rs
Black hole
Figure 21 The events in the
lifetime of a star depend on the
star’s mass.
Describe what happens to giant
stars when their cores collapse.
Determining the Age of
Stars Some groups of stars,
called clusters, contain stars
that all formed at the same
time. Scientists study these
stars through a telescope to
determine their color and
brightness. This information
can be used to find out how
far along each star is in its
life cycle. Because scientists know how long it
takes for different stars to
go through their life cycles,
the age of the star cluster
can be estimated.
458
The Lives of Stars
Scientists hypothesize that stars begin their lives as huge
clouds of gas and dust. The force of gravity, which causes
attraction between objects, causes the dust and gases to move
closer together. When this happens, temperatures within
the cloud begin to rise. A star forms when this cloud gets so
dense and hot that the atoms within it merge. This process is
known as fusion, and it changes matter to the energy that
powers the star.
After a star has formed, it continues to evolve. When a
medium-sized star like the Sun uses up some of the gases in its
center, it expands to become a giant star. Giants are large, cool
stars that have a red color. The Sun will become a giant in about
five billion years. At this time, it will expand to cover the orbits
of Mercury, Venus, and possibly Earth. It will remain that way
for about a billion years. Then, the Sun will lose its outer shell,
and the core will shrink to become a white dwarf star. A white
dwarf is a hot, small star. Eventually, the white dwarf will cool
and stop shining to become a black dwarf.
How long a star lives depends on how massive it is. Stars
more massive than the Sun complete their life cycles in shorter
amounts of time. The smallest stars shine the longest. Figure 21
illustrates how the course of a star’s life is determined by its size.
CHAPTER 15 The Solar System and Beyond
Supergiants When a large star begins to use
up the fuel in its core, it expands to become a
supergiant. These stars are similar to giant stars,
except they are much larger. Eventually, the core
of the supergiant will collapse. A huge shock
wave moves through the star, and the star
explodes and becomes bright. This exploding
star is called a supernova. For a few brief days,
the supernova might shine more brightly than a
whole galaxy. The dust and gas released by this
explosion, shown in Figure 22, might eventually
become part of a new star.
Meanwhile, the core of the
supergiant is still around.
If the core isn’t too large, it becomes a neutron
star. These are small objects that are extremely dense. However,
if the core is more than about three times as massive as the Sun,
it collapses rapidly to form a black hole, shown in Figure 23.
Light shone into a black hole disappears, and no light can escape
from a black hole.
Galaxies
If you travel far from city lights and point a telescope toward
the sky, you might see dim clumps of stars. These groups of stars
are called galaxies. A galaxy is a group of stars, gas, and dust held
together by gravity.
Types of Galaxies You now know how
planets and stars differ from one another.
Galaxies come in different shapes and sizes,
too. The three major types of galaxies are
elliptical, spiral, and irregular. These three
types of galaxies are distinguished by their
shapes. Elliptical galaxies are very common.
They’re shaped like huge footballs or
spheres. Spiral galaxies have arms radiating
outward from the center, somewhat like a
giant pinwheel. As shown in Figure 24,
some spiral galaxies have bar-shaped centers. Irregular galaxies are just that—irregular. They come in all sorts of different
shapes and can’t be classified easily.
Irregular galaxies usually are smaller than
other galaxies. They also are common.
Figure 22 This photo shows the
remains of a supernova.
Figure 23 A black hole has such
strong gravity that not even light
can escape. This drawing shows a
black hole stripping gas from a
nearby star.
Explain how black holes form.
Black hole
Disk of gas
Star
SECTION 3 Stars and Galaxies
459
Palomar Observatory
VISUALIZING GALAXIES
Figure 24
M
ost stars visible in the night sky are part of the Milky
Way Galaxy. Other galaxies, near and far, vary greatly
in size and mass. The smallest galaxies are just a few
thousand light-years in diameter and a million times more massive than the Sun. Large galaxies—which might be more than
100,000 light-years across—have a mass several trillion times
greater than the Sun. Astronomers group galaxies into four
general categories, as shown here.
▼
▼
SPIRAL GALAXIES Spiral
galaxies consist of a large, flat
disk of interstellar gas and dust
with arms of stars extending
from the disk in a spiral pattern.
The Andromeda Galaxy, one of
the Milky Way Galaxy’s closest
neighbors, is a spiral galaxy.
ELLIPTICAL GALAXIES
They are nearly spherical
to oval in shape and
consist of a tightly
packed group of
relatively old stars.
▼
▼
IRREGULAR GALAXIES Some
galaxies are neither spiral nor
elliptical. Their shape seems to follow
no set pattern, so astronomers have
given them the general classification
of irregular.
460
CHAPTER 15 The Solar System and Beyond
(bl)Royal Observatory, Edinburgh/Science Photo Library/Photo Researchers,
(others)Anglo-Australian Observatory
BARRED
SPIRAL GALAXIES
Sometimes the flat
disk that forms the
center of a spiral
galaxy is elongated
into a bar shape.
Two arms
containing many
stars swirl out from
either end of the
bar, forming what
is known as a barred
spiral galaxy.
s ar m
s arm
Cygnu
Per
ru
arm
us
e
s
C en
Ori
on a
rm
ta u
Sagittarius arm
Location of the Sun
The Milky Way Galaxy Which type of galaxy do you live in?
Look at Figure 25. You live in the Milky Way, which is a giant
spiral galaxy. Hundreds of billions of stars are in the Milky Way,
including the Sun. Just as Earth revolves around the Sun, stars
revolve around the centers of galaxies. The Sun revolves around
the center of the Milky Way about once every 225 million years.
Figure 25 The Sun is located
toward the edge of the Milky Way.
A View from Within You can see part of the Milky Way as a
band of light across the night sky. However, you can’t see the
whole Milky Way. To understand why, think about boarding a
Ferris wheel and looking straight up. Can you really tell what the
ride looks like? Because you are at the bottom looking up, you
get a limited view. Your view of the Milky Way from
Earth is like the view of the Ferris wheel from the bottom. As you can see in Figure 26, you can view only
parts of this galaxy because you are within it.
Figure 26 This is the view of the
Milky Way from inside the galaxy.
Infer why it is called the Milky Way.
Why can’t you see the entire Milky
Way from Earth?
The faint band of light across the sky that gives the
Milky Way its name is the combined glow of stars in
the galaxy’s disk. In 1609, when the Italian astronomer
Galileo looked at the Milky Way with a telescope, he
showed that the band was actually made of countless
individual stars. The galaxy is vast—bigger and
brighter than most of the galaxies in the universe.
Every star you see in the sky with your naked eye is a
member of the Milky Way Galaxy.
461
Frank Zullo/Photo Researchers
Corner mirror
Laser light
Moon
Earth
Figure 27 The constant speed
Speed of Light The speed of light is unique. Light travels
of light through space helps
astronomers in many ways. For
example, the distance to the Moon
has been determined by bouncing
a laser beam off mirrors left by
Apollo 11 astronauts.
through space at about 300,000 km/s—so fast it could go
around Earth seven times in 1 s. You can skim across ocean
waves quickly on a speedboat, but no matter how fast you go,
you can’t gain on light waves. It’s impossible to go faster than
light. Most galaxies are moving away from the Milky Way and a
few are moving closer, but the light from all galaxies travels
toward Earth at the same speed. The constant speed of light is
useful to astronomers, as shown in Figure 27.
Light-Years Earlier you learned that distances between the
Red Shift The Milky Way
belongs to a cluster of
galaxies called the Local
Group. Scientists have
determined that galaxies
outside of the Local Group
are moving away from
Earth. Based on this, what
can you infer about the size
of the universe? Research
the phenomenon known as
red shift and describe to
the class how it has helped
astronomers learn about
the universe.
462
planets are measured in astronomical units. However, distances
between galaxies are vast. Measuring them requires an even bigger unit. Scientists often use light-years to measure distances
between galaxies. A light-year is the distance light travels in one
year—about 9.5 trillion km.
Why is a light-year better than an astronomical
unit for measuring distances between galaxies?
Would you like to travel back in time? In a way, that’s what
you’re doing when you look at a galaxy. The galaxy might be
millions of light-years away. The light that you see started on its
journey long ago. You are seeing the galaxy as it was millions of
years ago. On the other hand, if you could look at Earth from
this distant galaxy, you would see events that happened here
millions of years ago. That’s how long it takes the light to travel
the vast distances through space.
CHAPTER 15 The Solar System and Beyond
The Universe
Each galaxy contains billions of
stars. Some might have as many
stars as the Milky Way, and a few
might have more. As many as 100
billion galaxies might exist. All these
galaxies with all of their countless
stars make up the universe.
Look at Figure 28. The Hubble
Space Telescope spent ten days in
1995 photographing a tiny sector of
the sky to produce this image. More
than 1,500 galaxies were discovered.
Astronomers think a similar picture
would appear if they photographed
any other sector of the sky. In this
great vastness of exploding stars,
black holes, star-filled galaxies, and empty space is one small
planet called Earth. If you reduced the Sun to the size of a period
on this page, the next-closest star would be more than
16 km away. Earth looks even lonelier when you consider that
the universe also seems to be expanding. Most other galaxies are
moving away at speeds as fast as 20,000 km/s. In relation to the
immensity of the universe, Earth is an insignificant speck of
dust. Could it be the only place where life exists?
Figure 28 The Hubble Deep Field
Image shows hundreds of galaxies
in one tiny sector of the sky.
Explain what this image indicates
about the sky.
How do other galaxies move relative to Earth?
Summary
Self Check
Stars
Constellations consist of stars that form patterns in the sky.
The Lives of Stars
Stars evolve through time.
How stars evolve depends on how massive
they are.
Galaxies
A galaxy is a group of stars, gas, and dust held
together by gravity.
You live in the Milky Way Galaxy.
The Universe
The universe might include 100 billion galaxies.
1. Explain why stars appear to move across the sky each
night. Why are some stars only visible during certain
seasons?
2. List and describe some constellations.
3. Describe the life cycle of a star like the Sun.
4. Think Critically Some stars might no longer be in
existence, but you still see them in the night sky. Why?
•
•
•
•
•
•
5. Convert Units A light-year is about 9.5 trillion
kilometers. Alpha Centauri is a star that is 4.3 lightyears from Earth. How many trillion kilometers away
is this star?
red.msscience.com/self_check_quiz
SECTION 3 Stars and Galaxies
463
R. Williams (ST Scl)/NASA
Design Your Own
Space Crlony
Goals
■ Infer what a space
colony might look like
on another planet.
■ Classify planetary
surface conditions.
■ Draw a space colony
for a planet.
Possible Materials
drawing paper
markers
books about the planets
Real-World Question
Many fictional movies and books
describe astronauts from Earth
living in space colonies on other
planets. Some of these makebelieve societies seem farfetched. So far, humans haven’t
built a space colony on another
planet. However, if it happens,
what would it look like?
Form a Hypothesis
Research a planet. Review conditions on the surface of the planet.
Make a hypothesis about the things that would have to be included in
a space colony to allow humans to survive on the planet.
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CHAPTER 15 The Solar System and Beyond
(t)Movie Still Archives, (b)NASA
Test Your Hypothesis
Make a Plan
1. Select a planet and study the conditions on its surface.
2. Classify the surface conditions in the following ways.
a.
b.
c.
d.
e.
solid or gas
hot, cold, or a range of temperatures
heavy atmosphere, thin atmosphere, or no atmosphere
bright or dim sunlight
unique conditions
3. List the things that humans need to survive. For example, humans
need air to breathe. Does your planet have air that humans can
breathe, or would your space colony have to provide the air?
4. Make a table for the planet showing its surface conditions and the
features the space colony would have to have so that humans could
survive on the planet.
5. Discuss your decisions as a group to make sure they make sense.
Follow Your Plan
1. Make sure your teacher approves your plan before you start.
2. Draw a picture of the space colony. Draw another picture showing the inside of
the space colony. Label the parts of the space colony and explain how they aid in
the survival of its human inhabitants.
Analyze Your Data
1. Compare and contrast your space colony with those of other students who
researched the same planet you did. How are they alike? How are they different?
2. Would you change your space colony after seeing other groups’ drawings?
If so, what changes would you make? Explain your reasoning.
Conclude and Apply
1. Describe the most interesting thing you
learned about the planet you studied.
2. Was your planet a good choice for a space colony?
3. Would humans want to live on your planet?
Why or why not?
4. Could your space colony be built using present
technology? Explain.
Present your drawing and your table to
the class. Make a case for why your planet
would make a good home for a space
colony. For more help, refer to the Science
Skill Handbook.
LAB
465
Mark Burnett
The Sun and the Moon
A Korean Folktale
The two children lived peacefully in the
Heavenly Kingdom, until one day the Heavenly
King said to them, “We can not allow anyone to sit
here and idle away the time. So I have decided on
duties for you. The boy shall be the Sun, to light
the world of men, and the girl shall be the Moon,
to shine by night.” Then the girl answered, “Oh
King, I am not familiar with the night. It would be
better for me not to be the Moon.” So the King
made her the Sun instead, and made her brother
the Moon.
It is said that when she became the Sun, the
people used to gaze up at her in the sky. But she
was modest, and greatly embarrassed by this. So
she shone brighter and brighter, so that is why the
Sun is so bright, that her modesty might be forever
respected.
Understanding
Literature
Cause and Effect The folktale explains
why the Sun and the Moon exist, as well as
why you should never look directly at the
Sun. No one is allowed to be idle in the
Heavenly Kingdom. This is a cause. What is
the effect?
Respond to the Reading
1. What was the purpose of this folktale?
2. What clues does the folktale give about
the personalities of the girl and the
King?
3. Linking Science and Writing Using
the form of a folktale, explain what
causes something that happens in
the solar system.
The cause-and-effect
relationships that
astronomers use to explain the origin of the
Sun and the Moon are different from what is
told in this folktale. Astronomers hypothesize
that the Sun formed from a collapsing cloud of
ice, gas, and dust. As the cloud contracted, the
temperature at its center became so high that
nuclear fusion began, and the Sun was born.
Many hypotheses about how the Moon formed
have been suggested. The most favored of
these suggests that the Moon formed from the
matter that was blasted into space when a
Mars-sized object struck Earth just after it
formed.
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CHAPTER 15 The Solar System and Beyond
Kevin Morris/CORBIS
Earth’s Place in Space
3. Meteorites are pieces of rock that fall to
Earth from space.
1. Day and night occur because Earth
rotates around its axis.
2. Earth’s axis is tilted about 23.5° from
straight up.
Stars and Galaxies
3. Earth’s revolution and Earth’s tilted axis
cause seasons to occur.
The Solar System
1. Apparent magnitude is a way to describe
how bright stars appear from Earth. It is
different from a star’s actual brightness, or
absolute magnitude.
1. The inner planets include Mercury, Venus,
Earth, and Mars.
2. Stars change throughout their lives. How
they change depends on how massive
they are.
2. The outer planets are Jupiter, Saturn,
Uranus, and Neptune.
3. There are four types of galaxies: elliptical,
spiral, irregular, and barred spiral.
Copy and complete the concept map below using the following terms: asteroid
belt, galaxy, universe, inner planets, comets and meteorites, and outer planets.
contains
includes
includes
contains
includes
Solar System
includes
are named
Jupiter
are named
Mercury
Mars
Venus
Earth
red.msscience.com/interactive_tutor
Saturn
Neptune
Uranus
CHAPTER STUDY GUIDE
467
(l)NASA, (r)National Optical Astronomy Observatories
Use the photo below to answer question 9.
astronomical unit p. 449
comet p. 454
constellation p. 456
eclipse p. 444
galaxy p. 459
light-year p. 462
lunar highlands p. 442
maria p. 442
meteorite p. 455
orbit p. 441
revolution p. 441
rotation p. 440
solar system p. 448
supernova p. 459
tides p. 445
Each question below asks about a vocabulary
word from the list. Write the word that best
answers each question.
1. What event occurs when Earth’s shadow
falls on the Moon or when the Moon’s
shadow falls on Earth?
2. Which Earth motion causes day and night?
3. What is a large group of stars, gas, and
dust held together by gravity called?
4. What is a group of stars that forms a
pattern in the sky called?
5. Which movement of Earth causes it to
travel around the Sun?
Choose the word or phrase that best answers the
question.
6. What is caused by the tilt of Earth’s axis and
its revolution?
A) eclipses
C) tides
B) phases
D) seasons
9. Why is Earth, shown above, a unique
planet in the solar system?
A) it is spherical
B) it has surface oceans
C) it has an elliptical orbit
D) it is the largest planet
10. How many galaxies could be in the universe?
A) 1 billion
C) 50 billion
B) 10 billion
D) 100 billion
11. Which results from Earth’s rotation?
A) night and day
C) phases
B) summer and
D) eclipses
winter
12. What unit is often used to measure long
distances in space, such as between stars
and galaxies?
A) kilometer
C) light-year
B) astronomical
D) meter
unit
13. How many planets are in the solar system?
A) six
C) eight
B) seven
D) nine
7. Which of the following is caused by the
gravity of the Moon and the Sun?
A) stars
C) comets
B) tides
D) maria
14. Which object’s shadow travels across part
of Earth during a solar eclipse?
A) the Moon
C) an asteroid
B) the Sun
D) a comet
8. An astronomical unit equals the distance
from Earth to which of the following?
A) the Moon
C) Mercury
B) the Sun
D) Pluto
15. If a star is massive enough, what can result
after it produces a supernova?
A) a galaxy
C) a black dwarf
B) a black hole
D) a white dwarf
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CHAPTER REVIEW
Royalty-Free/CORBIS
red.msscience.com/vocabulary_puzzlemaker
16. Compare and Contrast Which of the planets
in the solar system seems most like Earth?
Which seems most different from Earth?
Explain your answers using facts about
the planets.
22. Model Make a three-dimensional model
showing the relative positions of the Sun,
Earth, and the Moon during spring tides
and neap tides. Which moon phase
corresponds to each arrangement?
17. Predict How might a scientist predict the
day and time of an eclipse?
23. Poster Research the moons of Jupiter,
Saturn, Uranus, or Neptune. Make a
poster showing the characteristics of these
moons. Display your poster for your class.
18. Recognize Cause and Effect Which of the
Moon’s motions are real? Which are
apparent? Explain each.
19. Make and Use Tables Research the size,
composition, and surface features of
each planet. Show this information in a
table. How do tables help you to organize
information?
20. Make a model of a lunar or solar eclipse
based on what you have learned about
the Sun, the Moon, and Earth. Use simple
classroom materials.
Eclipses
kind
kind
can
see
moon
phase
can
sometimes
see
New
seen by
Use the graph below to answer question 26.
Light Curve of Delta Cephei
3.6
4.0
4.3
1
Lunar
moon
phase
a. Venus is 0.72 AU from the Sun. Neptune is
30.07 AU from the Sun. How many times
farther from the Sun is Neptune than Venus?
b. Jupiter is 5.20 AU from the Sun. Pluto is
39.48 AU from the Sun. How many times
farther from the Sun is Pluto than Jupiter?
25. Earth’s Circumference Earth’s diameter at
the equator is about 12,756 km. Using the
equation C d, where C is circumference,
d is diameter, and is about 3.14, calculate
Earth’s circumference at the equator.
Apparent
magnitude
21. Concept Map Copy and complete the following concept map using the following
terms: full, red surface, corona, solar,
and few.
24. Distances in the Solar System
seen by
Many
red.msscience.com/chapter_review
2
3
4 5 6 7 8
Time (days)
9 10
26. Variable Stars The brightness of some stars
varies with time. The graph above shows how
the apparent magnitude of a star named Delta
Cephei varies with time. What is the period of
this star’s light curve? Hint: The period is found
by determining the time between apparent
magnitude peaks.
CHAPTER REVIEW
469
Record your answers on the answer sheet
provided by your teacher or on a sheet of paper.
Examine the photo of the Moon below. Then, answer
questions 1–3.
7. Which of these terms refers to an alternate
rise and fall in sea level?
A. tide
C. eclipse
B. revolution
D. phase
8. Which of the following units is most useful
for measuring distances in the solar system?
A. kilometer
C. meter
B. light-year
D. astronomical unit
Use the diagram below to answer questions 9–10.
Z
Y
1. Which term refers to the dark, smooth
regions on the Moon’s surface?
A. lunar highlands C. maria
B. craters
D. rills
2. Which term refers to the light-colored,
mountainous regions on the Moon?
A. craters
C. rills
B. lunar highlands D. maria
3. What formed when meteorites struck the
Moon’s surface?
A. lunar highlands C. plateaus
B. maria
D. craters
4. Which planet is closest to the Sun?
A. Pluto
C. Mercury
B. Saturn
D. Earth
5. What is composed of ice and rock?
A. an asteroid
C. a meteorite
B. a comet
D. Venus
6. Which of the following is largest?
A. the universe
C. the Sun
B. the Milky Way D. the solar system
470
NASA
STANDARDIZED TEST PRACTICE
W
X
9. By which angle is Earth’s axis tilted?
A. 25°
C. 15°
B. 23.5°
D. 27.5°
10. Assuming the top of the diagram
represents north, which season occurs
in the northern hemisphere when Earth
is at position Z?
A. spring
C. summer
B. autumn
D. winter
Timing If you are taking a timed test, keep track of time during
the test. If you find that you’re spending too much time on a
multiple-choice question, mark your best guess and move on.
Record your answers on the answer sheet
provided by your teacher or on a sheet of paper.
Record your answers on the answer sheet
provided by your teacher or on a sheet of paper.
11. Explain how stars form. Write your answer
as several steps.
Use the illustration below to answer questions 22 and 23.
D
12. Describe the planet Earth. How is this
planet different from the other planets in
the solar system?
Sunlight
A
C
Earth
13. What is an asteroid? Where do many
asteroids occur in the solar system?
14. Explain how constellations are different
from galaxies.
15. How is a neutron star different from a
black hole?
16. How do the Moon and the Sun cause tides
to occur in Earth’s oceans?
17. How is Uranus’s axis of rotation different
from the axis of rotation of most other
planets?
The temperatures of stars usually are measured using
the kelvin scale. Use the equations below to answer
questions 18–21. °C represents degrees Celsius, and K
represents the temperature in kelvins.
°C K 273
K °C 273
18. The surface temperature of the Sun is about
6,000 K. How many degrees Celsius is this?
19. The cool supergiant Betelgeuse has a surface temperature of about 2,827°C. How
many kelvins is this?
20. A typical white dwarf star has a surface
temperature of 10,000 K. What is its surface temperature in degrees Celsius?
21. The lowest possible temperature is called
absolute zero. This temperature is 0 K.
What is this temperature in degrees Celsius?
B
22. Identify each lunar phase shown as A–D
in the diagram above.
23. Explain why the lunar phases change in a
cycle.
24. Describe the shapes of the planets’ orbits
around the Sun. How is Pluto’s orbit
different from the planets in the solar
system?
25. How are the characteristics of the inner
planets different from those of the outer
planets?
26. Summarize the life cycle of a very large
mass star. How is the life cycle of a very
large mass star different from the life cycle
of stars that have less mass?
27. Why does the same side of the Moon
always face Earth?
28. Why do the stars appear to move in the
sky each night?
29. Why are different stars visible during different seasons?
30. Explain how technology helps scientists
learn about the universe. List several different types of technology that are used to
study the universe in your answer.
red.msscience.com/standardized_test
STANDARDIZED TEST PRACTICE
471